U.S. Pat. No. 4,978,672 (referred to herein as '672, Indian Reference not available) provides 4-[alpha-(4-cyanophenyl)-1-(1,2,4-triazolyl)-methyl]benzonitrile and the process of its preparation. The patent discloses reacting 4-bromomethylbenzonitrile with 1,2,4-triazole to yield 4-[1-(1,2,4-triazol-1-yl)methyl]benzonitrile. 4-[1-(1,2,4-triazol-1-yl)methyl]benzonitrile is then reacted with 4-fluorobenzonitrile to give 4-[1-(4-cyanophenyl)-1-(1,2,4-triazol-1-yl)methyl]benzonitrile. This patent does not disclose the purity of 4-[1-(4-cyanophenyl)-1-(1,2,4-triazol-1-yl)methyl]benzonitrile, compound of formula 1. When we followed the patented process we also get the unwanted isomer 4-[1-(1,2,4-triazol-4-yl)methyl]benzonitrile, a compound of formula 4 (20 to 40%) in step 1. When the reaction mixture of step 1 is treated with 4-fluorobenzonitrile it yields 4-[1-(4-cyanophenyl)-1-(1,2,4-triazol-1-yl)-methyl]-benzonitrile, a compound of formula 1, and its isomer, a compound of formula 5. Thus the impurity of formula 4 has to be separated before treating it with 4-fluorobenzonitrile, which involves an additional step of column purification, which is reported in '672 and makes the process tedious and commercially unviable.

Further, if the intermediate contains an impurity like 4-toluonitrile or other related impurities, that are present in the raw material viz. 4-(bromomethyl)benzonitrile, in step 2, the impurities would participate in the reaction with 4- fluorobenzonitrile leading to the formation of 4-[1,1-Bis(4-cyanophenyl)methyl]benzonitrile (referred to herein as ‘tris impurity’) compound of formula 6 and other side products.
